Tactical, covert, nighttime combat and training flying missions are routinely conducted by military forces. In these operations, aircraft, particularly helicopters, fly in close formation along the contour of the landscape in order to avoid enemy radar, as well as to avoid early visual detection. Such operations are known as "ground-skimming" or "nap-of-the-earth" flights.
It is extremely difficult for pilots to see other aircraft flying in formation during covert, night-flying missions. Typically, these missions are conducted either at night or at dawn or dusk where natural lighting is at a minimum. In addition, since the purpose of such missions is to avoid detection, the aircraft fly with their navigation lights turned off. Further, the aircraft are usually painted with highly light-absorbent paint to make it even more difficult to see the aircraft at night. As a result, the risk of aircraft collisions is greatly increased.
To enhance the ability of pilots to see other aircraft in low-level light conditions, night vision goggles (NVG's), originally used by the army and infantry, were developed for military aviation. Generally, these goggles use tiny sensors to amplify electronically ambient light up to 100,000 times. Green images of night landscapes are displayed on two tiny video screens embedded in binocular-like goggles suspended from a pilot's helmet. Sophisticated infrared NVG's can provide images not only at night, but also in inclement weather.
However, due to the limitations in technology of NVG's, such goggles have not eliminated the risk of aircraft collisions. For example, military pilots mistakenly attempting to land on other aircraft is a common type of accident. Many problems associated with NVG's are due to the single-color lighting, limited field of view, and depth perception limitations of the goggles. Army Times reported in its Mar. 6, 1989 issue that between 1978 and 1989, 50 U.S. Army aircraft were involved in accidents where goggles were worn. These accidents cost the Army more than $114.6 million in lost aircraft and injuries. To this date, aircraft collisions are a constant concern for the military during such covert nighttime operations.
My earlier U.S. Pat. No. 4,916,581 discloses a device for illuminating the ends of a helicopter rotor blade by attachment of a chemiluminescent light stick to the rotor blade's tip. The chemiluminescent light provides an indication to the pilot of the helicopter of the position of the rotor blade's outer perimeter. However, such a system does not provide an indication to other pilots of the position and heading of the fuselage of the helicopter. Close formation flying operations require that pilots know the position of other aircraft and the direction or heading of the aircraft, which information allows pilots to track closely behind other aircraft in formation. With this information, pilots can swiftly and efficiently perform nap-of-the-earth flying missions.
Hard-wired, electric non-candescent position light systems are cost prohibitive. The installation of such a system would cost many thousand dollars per aircraft. Furthermore, such a system would require constant inspection to ensure its operability, would require regular replacement of defective bulbs or other hardware, and would be subject to unexpected failure during use.
The Army has attempted to use a tape-over system for covert, nighttime, training missions. The navigational lights, which are the red, green, and white lights on the aircraft, are taped over with a translucent tape so that a low-intensity light is given off. While such a system works satisfactorily in providing a low-intensity light, it is not entirely practical to use and sometimes is used in contravention of FAA regulations regarding aircraft lighting. When aircraft are required to fly through civilian airspace prior to or during training missions, the tape-over method cannot be used due to the FAA regulations regarding navigation lights. The aircraft must land when flying into civilian air space so that the tape can be removed and when flying out of civilian air space into military airspace so that the tape can be added. This delays the training mission and sometimes is not practical for lack of a suitable landing site.
Accordingly, a heretofore unaddressed need exists for a practical and cost-effective, low intensity anti-collision aircraft illumination system for covert night-flying operations.